Convert ide-cd to use scatterlists for PIO transfers and get rid of
partial completions (except on error) also for non-fs requests.

v2:
Do not map dataless commands to an sg since it oopses on the virt_to_page()
translation check when DEBUG_VIRTUAL is enabled.  (from Borislav Petkov,
reported/bisected-by Tetsuo Handa).

Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Acked-by: NBorislav Petkov <petkovbb@gmail.com>
Signed-off-by: NBartlomiej Zolnierkiewicz <bzolnier@gmail.com>